Touch panels of this type allow the area corresponding to the display screen of the display device to be used for both information display and information input thereby increasing the efficiency of utilization of that area. Therefore, the demand for touch panels of this type is becoming increasingly greater for use in small-size information processing devices and communication devices, in particular, portable communication terminals and the like.
FIG. 8 is a sectional view of a conventional touch panel assembly 1 including a front light unit 20 that is a kind of spread illuminating device. FIG. 9 is a sectional view showing a detailed structure of a touch panel 10 of the touch panel assembly 1 of FIG. 8. First of all, basically, the touch panel 10 comprises a pair of resistor layers (first and second resistor layers) 12 and 13 that are opposed to each other with a plurality of insulating dot spacers 11 interposed therebetween, and a transparent flat plate (e.g., transparent polyethylene terephthalate (hereinafter abbreviated as PET) film 16) for protection of the second resistor layer 13. The second resistor layer 13 is formed on the PET film 16, and the touch panel 10 is disposed in such a manner that the PET film 16 faces the display screen of a display device 30 such as a reflection-type color liquid crystal display device. The first and second resistor layers 12 and 13 are connected to each other at their peripheral portions by means of sealing members 14 for dust-proof and water-proof construction.
With the above structure, if the outer surface of the first resistor layer 12 is pressed, a pressed portion of the first resistor layer 12 is brought into contact with a portion of the second resistor layer 13 that is opposed to the pressed portion, and a signal corresponding to the contact position (i.e. pressed position) is generated.
In practice, a transparent layer (e.g., PET film 15) for protection of the resistor layer is also laid on the outer surface of the first resistor layer 12 and hence a pressing operation is performed actually on the PET film 15. Further, the PET film 16 is integrally attached to a touch panel support plate 17 that is a reinforcement member for securing sufficient strength (i.e., strength high enough to prevent a significant deformation of the second resistor layer 13 when the first resistor layer 12 of the touch panel 10 is pressed for operation). The touch panel support plate (reinforcement member) 17 is constituted by a transparent plate made of polycarbonate or the like, and is two or more times as thick as the touch panel 10 in the illustrated example. In other examples not shwon, the touch panel support plate 17 may be constituted by a glass plate, and also a thick glass plate (reinforcement member) may be used in place of the PET film 16 thus not providing the touch panel support plate 17 discretely.
As described above, the touch panel assembly 1 includes the front light unit 20. The front light unit 20 is adapted to irradiate light on the display screen of the display device 30 from its front side (i.e., from the display screen side) thereby illuminating the display screen brightly to enhance visibility. The front light unit 20 is disposed such that a light conductor plate 22 faces the display screen of the display device 30, and functions such that light emitted from a rod-like lamp 21 disposed beside the light conductor plate 22 is guided to be eventually irradiated onto the display screen of the display device 30 via the light conductor plate 22. The light that has reached the display device 30 is reflected either at the display screen or inside the display device 30, then passes through the light conductor plate 22 and the touch panel 10, and exits out thereby enabling displayed information on the display screen to be visible.
FIG. 10 shows basic components of the front light unit 20. The front light unit 20 is mainly composed of the light conductor plate 22 and the rod-like lamp 21, and is disposed in such a manner that the bottom surface of the light conductor plate 22 is opposed to the display screen of the display device 30 (see FIG. 8). The top surface of the light conductor plate 22 is formed with a light reflecting pattern that consists of a plurality of grooves 22a having a generally triangular cross-section and a plurality of flat portions 22b adjacent to respective grooves 22a. The interval between the grooves 22a of the light reflecting pattern varies depending on the position so that the brightness becomes approximately uniform at any positions of the light conductor plate 22 irrespective of the distance from the rod-like lamp 21. Specifically, the ratio of the width (occupation area) of the groove 22a to the width (occupation area) of the flat portion 22b is set so as to increase gradually as the distance from the rod-like lamp 21 increases. The grooves 22a of the light reflecting pattern that are formed on the light conductor plate 22 are very fine and hence cannot be recognized visually when one observes the screen. In another example, the light reflecting pattern may consist of only grooves (i.e., no flat portion is provided).
The rod-like lamp 21 is composed of a light conductor rod 23 that is a rod-like transparent member and a point light source 24 that is disposed adjacent to at least one of the two ends of the light conductor rod 23. The point light source 24 is a light-emitting diode. The light conductor rod 23 that is made of a transparent material is disposed along one end surface of the light conductor plate 22. The point light source 24 is disposed close to one end of the light conductor rod 23. On the other hand, the light conductor rod 23 is formed with an optical path changing means 23a. In the illustrated example, the optical path changing means 23a is such that grooves having a generally triangular cross-section are arranged in the longitudinal direction of the light conductor rod 23 in a predetermined manner.
The surfaces of the rod-like lamp 21 extending in the longitudinal direction, except for one surface opposed to the light conductor plate 22, are covered with a light reflecting member (reflector) 25 so that light is guided into the light conductor plate 22 with high efficiency. The light reflecting member 25 is a sheet-like member such as a film on which a metal such as silver is evaporated, a white film, or a film to which a white paint is applied, or a metal plate such as an aluminum plate that is mirror-finished and bent. As shown in FIG. 8, the rod-like lamp 21 that is covered with the light reflecting member 25 is further covered with a reinforcement frame 26 made of a metal such as stainless steel so as to be resistant to external impact.
As shown in FIG. 8, the components of the front light unit 20 are put and held together in place by means of a top frame 27 and a bottom frame 28 and are incorporated inside a portable communication terminal or the like. The top frame 27 and the bottom frame 28, each of which is a sheet metal part configured in an open-top box, can house the front light unit 20 and the display device 30 in an integral manner. The touch panel support plate 17 of the touch panel 10 is laid on the top surface of the top frame 27. The components are implemented as a unit in this manner, and hence the handleability in assembling or disassembling work can be increased. In this connection, in FIG. 8, reference numerals 41 and 42 denote double-sided adhesive tapes, reference numeral 43 denotes a cushion interposed between the reinforcement frame 26 and the display device 30, and reference numeral 31 denotes a polarizer plate that is usually provided on the display screen of the display device 30.
The conventional touch panel assembly 1 having the above configuration, however, has the following problems. First, the conventional touch panel assembly 1 is configured in such a manner that the touch panel 10 having the touch panel support plate 17 is laid on the top surface of the top frame 27, and this configuration, while giving advantages that the front light unit 20 and the display device 30 are protected from external force, the components are implemented as a unit, and that the touch panel 10 itself is surely provided with a sufficient strength, increases the total thickness thus making it difficult to reduce the size and the thickness of the touch panel assembly 1. As the total thickness increases, the distance between the display screen of the display device 30 and the touch panel 10 increases, and an observer more likely feels uncomfortable (the depth perception of the screen). If the touch panel support plate 17 is removed for reduction of the thickness, when the first resistor layer 12 of the touch panel 10 is pressed for operation, the second resistor layer 13 is deformed and brought into contact with the light conductor plate 22 possibly giving damages to the light reflecting pattern, which results in a problem that the functional performance of the light conductor plate 22 is deteroprated.
Where the touch panel support plate 17 is constituted by a glass plate, it is necessary to take a sufficient anti-impact measure to prevent breakage of the glass plate. Further, when the bottom frame 28 is screwed to a case (main body) of a communication terminal or the like, resin spacers must be disposed at screwing positions, which inevitably increases the number of components.
The present invention has been made in view of the above problems, and an object of the invention is therefore to achieve reduction in size and thickness of a touch panel assembly and also reduction of the number of components without deteriorating the functional performance of the touch panel assembly. Another object of the invention is to increase the degree of freedom in selecting the materials of components of the touch panel assembly to thereby make it possible to flexibly answer various requirements about products.